Telychian

In the geologic timescale, the Telychian is the third and final age of the Llandovery Epoch of the Silurian Period of the Paleozoic Era of the Phanerozoic Eon. The Telychian Age was between 438.6 ± 1.0 million years ago and 432.9 ± 1.2 Ma. The Telychian Age succeeds the Aeronian Age and precedes the Sheinwoodian Age. The name of the interval is derived from the Pen-lan-Telych Farm near Llandovery, Powys, Wales.
It ended with the Ireviken event.

Ireviken event

The Ireviken event was the first of three relatively minor extinction events during the Silurian Period. It occurred at the Llandovery/Wenlock boundary. The event is best recorded at Ireviken, Gotland, where over 50% of trilobite species became extinct; 80% of the global conodont species also become extinct in this interval.